Characterizing the spatiotemporal distribution of meteorological drought as a response to climate variability: The case of rift valley lakes basin of Ethiopia

Climate variability and recurrent meteorological droughts frequently affect the rain-dependent Ethiopian agriculture, where the rift valley lakes basin is one of the most drought-prone regions in the country. The aim of this study was to evaluate climate variability and characterize the spatiotemporal distribution of meteorological droughts using a merged satellite-gauge rainfall across the major agroecological zones (AEZs) of the rift valley lakes basin. To this end, coefficient of variation (CV) and standardized rainfall anomaly (SRA) were used to evaluate rainfall variability; Mann-Kendell test was used to examine trends of temperature and rainfall; and a grid-rainfall based standardized precipitation index (SPI) was used to assess the spatiotemporal distribution and severity of meteorological droughts. The SPI was computed for 37 years over 1981–2017 at 3-month and 4-month timescales for the bimodal rainy seasons. Finally, a higher inter-annual and spatial variability of rainfall and frequent meteorological droughts were found across the basin. Compared to the nationally documented historical drought years in the country, more frequent drought events were found in this basin, signifying its higher vulnerability to climate variability. As a result, between 1981 and 2017, the basin has partially experienced at least a moderate drought intensity on average every 1.68 and 1.76 years during the ‘Belg’ and ‘Kiremt’ season, respectively. Drought frequency was higher at the ‘Kolla’ AEZ, characterized by the highest CV of rainfall. Furthermore, these frequent droughts were accompanied by significant rising trends in monthly temperature. Such a warming trend, in this inherently warm area, coupled with expected global climate change scenarios could further aggravate drought conditions in the future. Moreover, the spatiotemporal distribution of drought events was found to be variable between and within AEZs in the basin so that more localized drought adaptation strategies could help to alleviate potential impacts. Thus, the drought history of each agroecological zone and the spatiotemporal distributions of recent droughts, this study has delivered, could enhance the awareness of concerned decision makers in tracing frequently affected locations, which could in turn enable them to design and implement improved water management techniques as a means of drought mitigation strategy.